whatsNext method
Returns the actual or preferred DecodingType of the encoded data for the given key or id.
Self-describing formats may return a DecodingType that indicates the type of the encoded data, or the preferred way of decoding it.
Non-self-describing formats may only return DecodingType.unknown for all types. In this case, the Decodable implementation must try the appropriate decoding method based on the expected type.
Implementation
@override
DecodingType whatsNext(String key, {int? id}) {
return _whatsNext(_value[key]);
}